The effect of fluctuations in an underdamped nonlinear oscillator on its absorption of an external periodic field at a subharmonic frequency has been investigated theoretically and with an analogue electronic circuit model. It is shown that the absorption is at its most pronounced when the eigenfrequency dispersion has an extremum. In such cases "resonances" with respect to noise intensity occur in two different frequency ranges of the external field, corresponding to two different ranges of noise intensity.